Optimisation of kombucha fermentation : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Food Technology, Massey University, Auckland, New Zealand. EMBARGOED until 9 February 2025.

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Kombucha is a slightly acidic, self-carbonated and refreshing fermented beverage made from sugared tea by the symbiosis of yeast and acetic acid bacteria (AAB). The symbiotic culture exists in a biofilm commonly called ‘symbiotic culture of bacteria and yeast’ (SCOBY) and fermented broth. Kombucha is popular in many regions of the world and its production relies on natural fermentation by an undefined complex mixed starter culture. Therefore, the fermentation process results in products of variable quality among the producers and even by the same individual processor. The efficiency of non-alcoholic Kombucha fermentation is determined by the final ethanol content, residual sugar and acidity at the end of fermentation. Kombucha beverages sold in the market are biologically active, therefore the fermentation continues during storage as the yeast and bacteria thrive on the residual sugar present in the final product. During storage, secondary fermentation generates the desired carbonation and also reduces residual sugar in the final products, but the microbial activity may also result in the production of beverages with higher alcohol levels than permissible. In New Zealand, Kombucha is categorised as a non-alcoholic beverage with alcohol of no more than 1.15% ABV or 0.5 % ABV (Australia). Kombucha brewers generally find it difficult to produce consistently high-quality products with low alcohol as stipulated by the Food Standards Australia New Zealand regulations. The present study aimed to optimise the fermentation process using robust experimental plans to produce a stable low alcohol fermented Kombucha with low sugar. The present research work was conducted in three Phases and the experiments were repeated twice with duplicate analyses.--Shortened abstract
Embargoed until 9 February 2025